Glass fibers intended for incorporation as reinforcing elements in articles fabricated from various matrix materials, such as polymeric as resinous materials, are usually provided with a light-weight size coating to protect the fibers from damage by abrasion during processing and fabrication and/or to enhance the reinforcing interaction between the fibers and the matrix material. Such size coatings typically comprise a film-forming polymeric or resinous component, a lubricant and a glass-resin coupling agent such as a partially hydrolyzable organosilane or hydrolysate thereof.
Such size coatings are usually deposited on the glass fibers during their production, which is ordinarily by attenuation of a plurality of streams of molten glass issuing from a reservoir through a corresponding plurality of orifices in a so-called bushing and solidification of the attenuated filaments by cooling. The coating is typically applied to the fibers as a liquid solution or dispersion in a volatile medium, from which the ultimate size coating is deposited on the fibers by evaporation of the medium and any other volatile components either before or after the fibers have been collected into a package as by winding onto a suitable collet.
Among the film-forming components of sizing compositions that have been employed are epoxy resins, especially where the fibers are to be used for reinforcing articles made from epoxy resins, such as by winding essentially continuous multi-filament glass fiber strands about a suitable form and impregnating with a curable resin composition and then curing the matrix resin to produce a glass fiber reinforced article such as a pipe or a tank. Both dilute solutions containing epoxy resin film-formers in volatile solvents such as diacetone alcohol and dilute emulsions of epoxy resin film-formers in aqueous media have been employed as sizing compositions for glass fibers. The use of large proportions of volatile organic solvents has disadvantages in that they are expensive and require careful handling during both use and disposal to avoid health and fire hazards. On the other hand, the use of aqueous media for the ordinary types of epoxy resins, i.e., those which have not been specially modified to render them soluble therein, requires that surfactants be employed to emulsify the epoxy resin and the surfactants employed are usually both non-volatile and detrimental to the properties of the ultimate reinforced article.
It is a principal advantage of the present invention that sizing compositions ae formulated as dilute emulsions of epoxy resin in aqueous media with reduced proportions of surfactants so as to avoid the disadvantages of using solvent-based sizing compositions while realizing superior properties in the ultimate reinforced articles.